1. Field of the invention
The invention relates to production of complex components made of metallic or ceramic materials, powders being used as the starting materials. The invention also addresses questions with regard to sintering and hot-isostatic pressing in respect of shrinkage.
The invention relates to the further development, perfection and simplification of powder-metallurgical production methods for the production of workpieces of comparatively complex shapes, where the problems of shrinkage during sintering play an important role. The field of application is, in particular, the component sector in turbine construction.
In a narrower sense, the invention relates to a process for shaping any desired component made of a metallic and/or ceramic material using a powder or a powder mixture as the starting material, the powder being filled loosely into a mold and then subjected to a sintering process.
2. Discussion of Background
Powders are used as the starting materials in numerous production methods in the metallurgical and ceramics industries. Powder-metallurgical processes have the advantage that virtually any desired shape can be achieved. The intention is to produce workpieces by powder metallurgy as finished articles in order to be able to save on some or all expensive machining costs. The starting materials in all of the known processes for obtaining net shapes or near-net shapes of the workpieces are slurries (slip, paste) of powders in solvents using a binder. The following are used as additives to powder mixtures:
water+binder+additive (slip casting, freeze drying).
water+cellulose (metal-powder injection molding (MIM) by the Rivers process).
thermoplastics (metal-powder injection molding).
With all of these wet-mechanical methods numerous difficulties arise with regard to quality, freedom of shaping, reproducibility and choice of the composition:
Bubble formation when mixing powder with binder and solvent.
Restriction of the wall thickness of the workpieces pieces (for example max. 5-10 mm for "MIM"), since otherwise the binder can no longer be completely removed.
The occurrence of binder residues (for example carbon), which, even after "burning out" the binder, remain behind in the workpiece and can impair its composition in an uncontrolled manner.
The necessity for fresh selection/fresh development of the binder when changing to other shapes and/or compositions of the workpieces.
The following publications are cited in respect of the prior art:
GB Pat. Appl. 2088414.
EP Pat. Appl. 0191409.
R. Billet, "PLASTIC METALS: From Fiction to Reality with Injection Molded P/M Materials", Parmatech Corporation, San Rafael, Calif., P/M-82 in Europe Int. PM-Conf. Florence I 1982.
Goran Sjoberg, "Powder Casting and Metal Injection Moulding", manuscript submitted to Metal Powder Report September 1987.
The known processes leave something to be desired. There is therefore a need for improvement and further development of the powder-metallurgical/powder-ceramic production methods.